Aqueous process for preparing polyamic acids and polyamic acid related gel materials

Abstract

The present disclosure is directed to methods of forming polyamic acid, polyamic acid metal salt, and polyimide gels under aqueous conditions, the methods utilizing water-soluble carbonate or bicarbonate salts. These gels may be converted to aerogels or xerogels, which may further be converted to carbon aerogels or xerogels. Such carbon aerogels or xerogels have the same physical properties as carbon aerogels or xerogels prepared from polyimide aerogels obtained according to conventional methods, i.e., organic solvent-based methods.

What is claimed is: 
     
         1 . A method of preparing a polyimide aerogel, the method comprising:
 combining in water a water-soluble diamine, a water-soluble carbonate or bicarbonate salt, and a tetracarboxylic acid dianhydride;   allowing the components to react, providing an aqueous solution of a salt of a polyamic acid;   imidizing the polyamic acid salt to form a polyimide wet gel, wherein imidizing the polyamic acid salt comprises adding a gelation initiator to the aqueous solution of the polyamic acid salt to form a gelation mixture and allowing the gelation mixture to gel; and   drying the polyimide wet gel to form the polyimide aerogel.   
     
     
         2 . The method of  claim 1 , wherein the combining comprises:
 dissolving a water-soluble diamine in water to form an aqueous diamine solution;   adding the water-soluble carbonate or bicarbonate salt to the aqueous diamine solution;   adding a tetracarboxylic acid dianhydride to the aqueous solution of the diamine and the water-soluble carbonate or bicarbonate salt to form a solution; and   stirring the solution for a period of time in a range from about 1 hour to about 4 days at a temperature in a range from about 4 to about 60° C.   
     
     
         3 . The method of  claim 1 , wherein the combining comprises:
 dissolving a water-soluble diamine in water to form an aqueous diamine solution;   adding a tetracarboxylic acid dianhydride to the aqueous diamine solution to form a suspension;   stirring the suspension for a period of time in a range from about 1 hour to about 4 days at a temperature in a range from about 4 to about 60° C.;   adding the water-soluble carbonate or bicarbonate salt to the suspension; and   stirring the suspension for a period of time in a range from about 1 hour to about 4 days at a temperature in a range from about 4 to about 60° C. to provide the aqueous solution of the salt of the polyamic acid.   
     
     
         4 . The method of  claim 1 , wherein the combining comprises:
 adding to water, simultaneously or in rapid succession, a water-soluble diamine, a tetracarboxylic acid dianhydride, and the water-soluble carbonate or bicarbonate salt; and   stirring the resulting mixture for a period of time in a range from about 1 hour to about 4 days at a temperature in a range from about 4 to about 60° C. to provide the aqueous solution of the polyamic acid salt.   
     
     
         5 . The method of  claim 1 , wherein the water-soluble carbonate or bicarbonate salt comprises lithium, sodium, potassium, ammonium, or guanidinium cations. 
     
     
         6 . The method of  claim 1 , wherein the water-soluble carbonate or bicarbonate salt is selected from the group consisting of lithium carbonate, lithium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, ammonium carbonate, ammonium bicarbonate, guanidinium carbonate, and combinations thereof. 
     
     
         7 . The method of  claim 1 , wherein:
 the water-soluble carbonate or bicarbonate salt is a carbonate, and a molar ratio of the water-soluble carbonate salt to the diamine is from about 1 to about 1.4; or   the water-soluble carbonate or bicarbonate salt is a bicarbonate, and a molar ratio of the water-soluble bicarbonate salt to the diamine is from about 2 to about 2.8.   
     
     
         8 . The method of  claim 1 , wherein a molar ratio of the tetracarboxylic acid dianhydride to the diamine is from about 0.9 to about 1.1. 
     
     
         9 . The method of  claim 1 , wherein the tetracarboxylic acid dianhydride is selected from the group consisting of biphthalic dianhydride (BPDA), benzophenone tetracarboxylic dianhydride (BTDA), oxydiphthalic dianhydride (ODPA), napthanyl tetracarboxylic dianhydride, perylene tetracarboxylic dianhydride, and pyromellitic dianhydride (PMDA). 
     
     
         10 . The method of  claim 1 , wherein the diamine is 1,3-phenylenediamine, 1,4-phenylenediamine, or a combination thereof. 
     
     
         11 . The method of  claim 1 , wherein the diamine is 1,4-phenylenediamine. 
     
     
         12 . The method of  claim 1 , wherein a range of concentration of the polyamic acid salt in the aqueous solution is from about 0.01 to about 0.3 g/cm 3 , based on the weight of the polyamic acid. 
     
     
         13 . The method of  claim 1 , wherein the water-soluble carbonate or bicarbonate salt is guanidinium carbonate, and wherein the solution of the salt of the polyamic acid exhibits thixotropic behavior. 
     
     
         14 . The method of  claim 1 , further comprising adding an electroactive material to the aqueous solution of the polyamic acid salt. 
     
     
         15 . The method of  claim 14 , wherein the electroactive material comprises carbon, graphite, silicon, sulfur, Prussian blue, lithium iron phosphate, a combination thereof, or a one or more precursors of any thereof. 
     
     
         16 . The method of  claim 1 , wherein the gelation initiator is acetic anhydride. 
     
     
         17 . The method of  claim 1 , wherein drying the polyimide wet gel comprises:
 optionally, washing or solvent exchanging the polyimide wet gel; and   subjecting the polyimide wet gel to elevated temperature conditions, lyophilizing the polyimide wet gel, or contacting the polyimide wet gel with supercritical fluid carbon dioxide.   
     
     
         18 . The method of  claim 1 , further comprising converting the polyimide aerogel to an isomorphic carbon aerogel, the converting comprising pyrolyzing the polyimide aerogel under inert atmosphere at a temperature of at least about 650° C. 
     
     
         19 . A polyimide aerogel prepared by the method of  claim 1 , the polyimide aerogel comprising a residual amount of the water-soluble carbonate or bicarbonate salt. 
     
     
         20 . A carbon aerogel prepared by the method of  claim 18 .